Objective: To compare the imaging findings among pyogenic, fungal and tuberculous abscess using conventional, diffusion-weighted imaging [DWI], and susceptibility-weighted magnetic resonance sequences [SWMRS].

Materials and Methods: A retrospective study was done in 43 patients with diagnosis of brain abscesses between January 2004 and January 2016 whose MRIs of the brain were available. Imaging characteristics on conventional MRI, DWI, and SWMRS were recorded in all abscesses.

Results: The present study included 43 examinations. The pyogenic abscesses had smooth or lobulated walls (82%) with complete hypointense T2 rim (95.4%), whereas fungal abscess showed crenated walls (66.7%) with intracavitary projections (n = 6/12) and heterogeneous DWI cavity (83.3%). Tuberculous abscess had smooth/lobulated wall (77.8%) or crenated wall (22.2%) with heterogeneous (50%) or homogeneous (50%) hyperintense DWI cavity. Dual rim sign, previously described as a specific sign for pyogenic abscess, was present in 6/13 cases of pyogenic brain abscess. This sign was also found in 2/9 cases of fungal brain abscess and 2/3 cases of tuberculous brain abscess. There was no statistically significant difference between mean ADC value of a wall, restricted portion and non-restricted portion of the cavity among pyogenic, fungal and tuberculous brain abscesses. However, fungal and tuberculous abscess had a higher proportion of cases with non-restricted portion within the cavity.

Conclusion: Combination of imaging findings in conventional, DWI, and SWMRS, differentiation among pyogenic, fungal and tuberculous abscess might be possible. “Dual-rim sign”, previously described in pyogenic brain abscess, is not specific for pyogenic. This sign can be found in tuberculous and fungal abscess.

Keywords: Brain abscess, Diffusion-weighted imaging, Susceptibility-weighted MRI sequences